I use Facebook the most for promotion, it brings the most relevant people to whatever I am promoting on there, for example YTtalk, if I post an update on there, those who have liked the page will be reminded the forums are here and to come back and that sort of promotion is invaluable to someone who owns a website or someone who is promoting their videos, if you have a fan base and they like you over on Facebook, when they sign into it they will see your latest videos which they are normally interested in watching because they took their time to like your page.
Second to Facebook I use Twitter, I aint such a fan of Twitter but it can help bring in extra views although these are people who are already following usually or people who are already interested.
As for promoting to those who dont know about you/your channel I think sites like that younow.com is great for musicians because you're able to share your music live. Sites that are similar to younow but say for comedy I think would work very well especially if they pull in non-musicians to watch regularly.
One thing many dont even bother with is promoting themselves on YouTube itself, that's where almost all the viewers currently are and whether youre promoting yourself by commenting on peoples videos, doing video responses, networking with others, collaborating or getting that shoutout because you helped someone, you will almost always find people interested in your videos/content.
I think the most productive forums you could possibly promote on are those that are related to your niche, say you do computer hardware videos, then a computer forum is relevant, say you do Xbox modding, an Xbox modding forum is relevant and in your case JTA then a Photography forum would be most relevant. Thats where many of your potential viewers are.
If you are wanting to get your name out there on all the video upload sites then you could do just that, theres a site that allows you to share them to every last one of the more or less but it does charge you for using it, I forget its name now but that is something I think people here could be interested in, as we all know YouTube isnt the only place where you can post your videos to and isnt the only place your potential audience is.
I know that one! It's supposed to have these two really cool guys 'Vic' and 'Joe' who are like uber popular 
